The current longitudinal study of infant vocal development has yielded important new information on early differences between normally developing an handicapped infants. Down syndrome and deaf infants show clear anomalies in vocal patterning in the first year of life, and there is preliminary reason to believe that other disorders (e.g., autism) may also be marked by early vocal abnormalities. The proposed renewal of the vocal development effort would focus on deepening the study of early markers of linguistic handicap, by expanding the frames of description of vocal development. In addition to Down syndrome and deaf infants, the proposed study would focus on autistic and other mentally retarded children. Whereas the prior work treated vocalizations as independent events, the proposed work will consider them in the interfactional context of parent- infant dialogues and the interplay of experimenters and children. Whereas the prior work treated vocalizations in terms of sound quality only, the proposed work will study the primitive communicative functions that may be served by vocalizations. Whereas the prior work treated syllable-like vocal expression only, the proposed work will also describe intonation, facial affect and gesture. Within the expanded frames of evaluation, it is anticipated that the proposed work will yield new means of identifying characteristics of disorders early in life and may also yield implications regarding appropriate interventions.